Hydrogen is one of the most promising alternative energy sources. It can be obtained by electrolysis of water, which is environmentally friendly and efficient. However, the electrolysis of water is an energy intensive process, which is very expensive. On the other hand, photolysis, the splitting of water by light, presents an attractive alternative method of obtaining hydrogen. Additionally, light driven reduction of carbon dioxide by water to provide hydrocarbons or methanol may be another promising alternative to alternate energy sources. For both types of reactions, coupled water oxidation to oxygen is required. In order to facilitate the photolysis of water by light in either type of reaction, a catalyst is required for the reaction. However, there are very few catalysts found to be efficient and cost effective to carry out this reaction. (See, Molecular, Catalysts for Water Oxidation, Yagi et al, Chem. Rev., 101, 21-35 (2001)). For example, Gratzel et al., described that Ruthenium dimers can be used as catalysts for water oxidation. (See U.S. Pat. No. 5,223,634 to Gratzel et al.). More recently, Brimblecombe et al. have discovered that tetra-manganese-oxo cluster can also be used to catalyze water oxidation. (See PCT application WO 2008/116254 to Brimblecombe et al.). However, these catalysts are limited to the scope and ability to harness the photo chemical reactions.
Therefore, there is a need in the industry for an efficient catalyst for the electrolysis or photoelectrolysis of water to obtain hydrogen or water reduction of carbon dioxide to obtain affordable and sustainable alternative source of energy.